1. Field of the Invention
The present invention relates to a photoelectric conversion device, specifically, a photoelectric conversion device formed using a thin film semiconductor element and a manufacturing method thereof. Further, the present invention relates to electronic devices using a photoelectric conversion device.
2. Description of the Related Art
A number of photoelectric conversion devices generally used for detecting an electromagnetic wave are known, and for example, a photoelectric conversion device having sensitivity in ultra-violet rays to infrared rays are referred to as a photo-sensor in general. A photo-sensor having sensitivity in a visible radiation region with a wave length of 400 nm to 700 nm is particularly referred to as a visible light sensor, and a large number of visible light sensors are used for devices which need illuminance adjustment or on/off control depending on a human living environment.
In particular, in a display device, brightness in the periphery of the display device is detected to adjust display luminance. This is done because unnecessary electric-power can be reduced and visibility can be enhanced by detecting peripheral brightness and obtaining appropriate display luminance. Specifically, such a photo-sensor for adjusting luminance is used for a cellular phone or a personal computer (for example, Reference 1: Japanese Patent Laid Open No. 2003-60744).
In addition, as well as peripheral brightness, luminance of a back light of a display device, particularly, a liquid crystal display device is also detected by a photo-sensor to adjust luminance of a display screen (for example, Reference 2: Japanese Patent No. 3171808 and Reference 3: Japanese Patent No. 3193315).
Further, in a display device using a projector, the convergence adjustment is conducted by using a photo-sensor. The convergence adjustment is to adjust an image so that an image of each color of RGB does not generate discrepancy. By using a photo-sensor, a location of an image of each color is detected, and the image is arranged in the right location (for example, Reference 4: Japanese Patent Laid Open No. 2003-47017).
FIG. 2 shows a structure of a photoelectric conversion device that has been used conventionally. In FIG. 2, an electrode 1002 is formed over a substrate 1001, and a p-type semiconductor layer 1003, an intrinsic semiconductor layer 1004 (also referred to as an i-type semiconductor film) and an n-type semiconductor layer 1005, which serve as a photoelectric conversion layer, are formed over the electrode 1002. Further, an electrode 1006 is formed over the n-type semiconductor layer 1005. Then, an insulating film 1007 is formed to cover the electrodes 1002 and 1006. Moreover, a first extraction electrode 1012 connected to the electrode 1002 and a second extraction electrode 1013 connected to the electrode 1006 are formed over the insulating film 1007.
However, it is known that in the photoelectric conversion device having the structure shown in FIG. 2, a leakage current occurs in some cases where the photoelectric conversion device operates for a long time. The occurrence of the leakage current is caused, because a crack 1021 is produced in the photoelectric conversion layer, in particular, in a corner portion (step portion) of the i-type semiconductor layer 1004, and the portion becomes a leakage path.
FIGS. 22A to 22C shows photographs of a conventional structure taken by an electronic microscope. As shown in FIGS. 22A to 22C, it can be known that a crack is generated in a corner portion (a step portion) of an i-type semiconductor layer. When an electric field concentrates on this crack, defects such as occurrence of leakage current are caused.